Process for the dehydrogenation of hydrocarbons



Feb. 1 9, 1946. w. A. scHuLzE ET Al.

' PROCESS FOR THE DEHYDROGENATION 0F HYDROCARBONS 2 sheets-sheet 1 FiledMay 6, 1943 l ATTORNEYS4 Feb. 19, 1946. w. A. scHULzE E'rAl.

PVROCESS FOR THE DEHYDROGENATION OF HYDROCARBONS 'Filed May 6,/1943 2Sheets-Sheet 2 INVENToRs W A SCHULZE `1 c. HILLYEB ATTORNEYS PatentesFeb. 19,1946

' uNlrrzo STAT PROCESS FOR DEHYDROGEATION F HYDROCARBONS waiter A.Schulze and Johnc. muyer, Bartlesvllle, Okla., assignors to PhillipsPetroleum ES PATENTl Company, a corporation of Delaware Application May6, 1943, Serial No. 485,908

' V12 Claims. (Cl. Zim-680) butane to butenes in a first dehydrogenationstep and dehydrogenation of a butene to butadiene in a seconddehydrogenation step.

'I'his is a continuation-impart of the copending application Serial No.358,008 iiled September 23, 1940, now Patent No. 2,362,218, issuedNovember 7, 1944, disclosing a process in which butene-2 obtained fromthe catalytic dehydrogenation of normal butane is separated andsubsequently dehydrogenated to produce butadiene. 'I'he presentinvention is directly concerned with the recovery of butene-Z from bothstages of dehydrogenation and particularly with the catalyticisomerization of butene-l concurrently formed to promote the.

eiliciency oi' product segregation from both of said stages ofdehydrogenation.

An object of this invention is to provide an improved process for theproduction of a diolefln from the corresponding paramn.

Another object of this invention is to' provide another arrangement ofapparatus for carrying out the process of this invention.

It hasI been proposed to produce butadiene by the catalyticdehydrogenation of normal C4 parailins, oleiins, and mixtures thereof,with various methods being suggested to enable the provision vofsuitable butylene concentrations in thedehydrogenation feed stocks. Suchmethods have included the dehydrogenation of normal butane to yieldparaflin-oleiin mixtures, and the treatment Y of said mixtures im thesame or diilerent dehydro- -genation steps to ".further econvert theoleilns to the dioleiins. Other methodshave indicated improved.eillciency and economy from the segregation of normal butylenes fromunconverted paraflins prior to conversion to produce the dioleiin.

f The latter methods have been preferred generally such a process whichis particularly applicable to the production of butadiene from butane.

Still another object of this invention is to prol vide an improvedprocess for the production of butadiene from butane in which thebutene-l, formed concurrently withl the formation of butene-2, isconverted to butene-Z.

A further object of this invention is to provide an improved method forthe separation of butene- 2 and butadiene from the products of thecatalytic dehydrogenation of C4 hydrocarbons.

A particular advantage of the process of the present invention is thatit provides for the extraction of butadiene and butene-2 from theemuents of .both dehydrogenation steps in a single operation.

Other objects and advantages of the invention will be apparent to thoseskilled in the art from a consideration of the following detaileddisclosure and the accompanying drawings.

Figure 1 of the drawings is a diagrammatic ele-A vational view of anarrangement of apparatus suitable for carrying out the presentinvention.

Figure 2 is a diagrammatic elevational view 0f for the reason that theoptimum' dehydrogenation conditions for the parafn-oleiin and theolefindiolen conversions are distinctly di'erent, and overall processyields and economics have favored the relatively complete segregation ofbutylenes as the feed stock to the olefln-diolen conversion step.

Heretofore, means for accomplishing butylene segregation orpurificationv from n-butane have been handicappedv by the physicalproperties of the two isomers, butene-l and butene-2 produced in thedehydrogenation reactions. theseproperties, and particularly thoseoibutene- 1, have complicated the separation butadiene as the endproduct of the manufacturing process.

In our copending application, Serial No. 358,008,

referred to above, we have disclosed an improved method for producingbutene-Zas the feed stock to a second dehydrogenation step by means ofcatalytic isomerlzation of butene-l to but'ene-Z. However, in saidsecond step, theyre-establishment of the equilibrium between the normalbutylene isomers at the temperature level of the dehydrogenation withformation of increased amounts of rbutene-l has resulted in increaseddifficulty-in butadiene separation and puriiication, and also in lthepresence of considerable amounts of butene-l in butylene mixturesrecycled to the saidsecond dehydrogenation step.

We have now discovered a process whereby both butadiene puriiication andbutylene segregation steps 'are accomplished more eillciently and thebutylene feed to the second dehydrogenation stage 4 comprisesessentially butene-2. This last-named improvement has been found toresult in improved butadiene yields due .apparently to the more sat-Furthermore,v

and recovery of the olen-diolefln conversion step.

It is anfadditional feature of our new process that the basic operationsare cooperative to an unusual degree, and may, if desired, be carriedout in units of process-equipment serving both stages ofdehydrogenation. 'This advantage may be utilized to reduce the equipmentrequirements and operating costs for butadiene production at the samethat improved yields are obtained as a result of the present invention.Y

In one specific embodiment, our process comprises the following steps:(1) normal butane is catalytically dehydrogenated in a firstdehydrogenation stage to produce normal butylenes; (2) thebutane-butylene condensate from step 1 is catalytically isomerized toconvert butene-l to butene2; .(3) the effluent from the isomerizationtreatment is treated by solvent extraction or frac.. tionation toseparate butene2 from the-other C4 components which include unconvertedn-butane tov be recycled to the first dehydrogenation stage: (4) thebutene2 is catalytically dehydrogenated in a second stage to producebutadiene; (5) the C4 condensate from step 4 is treated with a selectivesolvent to separate butadiene and butene2 from butne-l and butane; (6)the butadienebutene2 mixture is fractionated to separate substantiallypure butadiene from butene2; (7) the butane-butene-l stream is passed`to the isomerization unit and the butene2 produced is recovered withthat derived from the first stage dehydrogenation. Y

In additionto these basic operations, several*l other auxiliary stepsmay be desirable in some circumstances. These may include a furtherfractionation oi. the n-bu'tane-butened mixture being recycled to therst stage of dehydrogenation to yrecover and isomerizefurther quantitiesof butene-l, or the treatment of the recycle streams to eitherdehydrogenation stage to remove small amounts oi' higher boiling liquidand/or isobutylto butenes. The ei'lluent of the ilrst stage of thedehydrogenation comprises unconverted butane isfactory 'characteristicsof butene-Zas feed t g maining in the n-butane recycle stream may becarried out in unit 5. This unit may be a simple fractionating columnwith the butylenes taken overhead and returned through line to eitherth'e isomerization unit 5 or the' isobutylene removal unit 29. Then-butane from fractionator l f is then recycled through line I0 to thefirst stage dehydrogenation.

'I'he butene2 is stripped from the solvent in 'stripper II and passesthrough line I2 to be A feed stream comprising fresh and recycle butene2is catalytically dehydroganated in unit I3 under conditions selected toeilect partial conversion to butadiene, and the dehydrogenation productsare cooled, compressed, and treated in units I4 and I5 to collect a`C4condensate comprising butadiene and butylenes.

The second stage C4 condensate then vpasses to column IBin which apartial removal of butene2 along with traces of heavier liquid iscarried out. The overhead product from this fractionation passes throughline Il to absorber I8, while the bottoms fraction is taken through lineI9 tov a subsequent depentanizing or stripping operation in column 25.

The absorberx I8 operates with a selective solvent for butene2 andbutadiene, and these components are separated from the stream enteringby line Il. The unabsorbed portion comprising butene-l and smallerquantities of isobutyle'ne and n-butane formed over the second stagecatalyst passes out through line 20. Some butene2 may also passthroughand be recovered in subsequent processing. When isobutyleneremoval is practised, the stream may pass through removal unit 28 forselective polymerization treatment or 't ing through line 20.

and normlbutylenes, butene-l and the 2'bu l tenes, together with C3` andlighter hydrocarbons,

Cs and heavier hydrocarbons, and some isobutylene. Th'e reiiluent of thedehydrogenation is cooled, as, by the cooler 3, and passed to aseparation step, designated by the numeral l, wherein the eiiiuent issubjected to compression and cooling to form condensate while at thesame time the Cs and heavier vhydrocarbons and the, C: vand lighterhydrocarbons are separated from the C4 hydrocarbons. The 'C4 hydrocarbonstream, which may advantageously contain a part of the C: and/or lighterhydrocarbonsis passed to the isomerization step 5 where conversion ofbutene-'1` present in the stream to the butene-Zisomers is `effected inthe presence of a suitable' catalyst. The egluent from ,unit 5 passes toabsorber 'I where a selective solvent is utilized to absorb the butene2,while a stream oi' predominantly n-butane with a greatly reducedbutene-l content passesv through line 8 to be recycled to the' firststage dehydrogenation. Optionally, treatment t0` separate relativelysmall amounts of butene-l reyso The butene2 and butadiene are strippedfrom the solvent in stripper 2| and pass through line 22 to butadienecolumn 23u. In this column substantially pure butadiene. is takenoverhead through line 24 to storage, while butene2 is removed as thebottoms product through line I5 to column 25. 'This column 25 may beused to fractionate the total recycle butene2 from the botv toms ofcolumns Il and 23, with recycle butene2 taken overhead throughlines '2land `I2 to the second stage dehydrogenation unit. Alternately, thebutene2 from the bottom of column 2l may be recycled directly throughlines 21 and I2.

In Figure 2 a variation in the sequence of th'e same basic processstepsis shown whereby a singl solvent absorption unit is utilized to treatthe C4 condensate from both stages of dehydrogenation. In thisarrangement, the products' of n ormal butane dehydrogenation in unit 2are treated to recover va predominantly C4 condensate com- The seconddehydrogenation stage operating on a predominantly butene2 feedobtained' as de-v A'Ci scribed hereinafter is indicated by unit is.condensate comprising normalbutylenes and butadiene is collected in unitl5. This condensate -passes to fractionator I8 where partial removal ofbutene-Z along withtraces of higher boiling liquid is accomplished.'I'he overhead product from column I8 passes through line 32 to absorberremaining butene-2. I .y

The unabsorbed hydrocarbons from absorber 1 comprise n-butane andbutene-l from both the first and second stages of dehydrogenation. Thismixture passes through line 8 to column 9 which is operated to produce abottoms product of substantially olen-free n-butane removed through'line IU as recycle stock for the first stage dehydrogenation. Theoverhead fraction taken -1 for selective absorption of butadiene and the1- hydrogenation stage.

through line 30 contains butene-l together with any isobutylene formedduring dehydrogenation, and some n-butane may be included depending onthe precision of the fractionation.

Said overhead fraction in line lsv-returned I to isomerization unit 5for further conversion of butene-l to butene-2. 'I'he stream or aportion thereof may be passed intermittently or continuously to unit 29for the removal of isobutylene by selective polymerization', or the liketo prea vent the building-up of isobutylene in the system. The butene-2produced by isomerization of recycled butene-l is thus combined withthat rescribed feature the use of catalytic momerization to reducefractionation requirements for butene- 1 separation and are particularlyadapted to the utilization of solvents exhibiting relatively greatersolubility for 2olens than for l-oleiln. In theV in the conversion of asubstantial proportion of the butane to the corresponding 'oleiina Othersources loi' butylenes may of course be utilized if available, althoughpreliminary purification steps.

e.l s. isobutylene separation, may be required.

The dehydrogenation catalysts and conditions for theparaiiin-oleiin'conversioxi are chosen 'to v yield adequate amounts ofolens at reasonable covered from the two dehydrogenation operations,land the amount of butene-l separated in column 9 is controlled by thecompleteness of con version in unit 5.

'Ihe rich solvent from absorber I is stripped instripper Il to removebutene-Z and butadiene. This mixture then passes to butadiene column 23which operates to separate substantially pure bu- ,diene as the overheadproduct.k The butadiene is removed through line 24 to storage, while thebutene-2 bottoms fraction is taken through line I2 yand combined withthe butene-2 from column y 25 as feed to the second dehydrogenationstage.-

This last-named column 25 -serves to strip butene-2 from higher boilingliquids in the bottoms fraction from column I 8. Ifnecessary, .theentire .butene-Z stream may be similarly treated in column 25.

Other possible .alternatives are illustrated in j Figure 2 forapplication in special circumstances.

l' lThus, in some cases depending on the butadiene concentration in thestream and the particular isomerization catalyst, it may be desirable topass the butadiene-butylene mixture from fractionator I6 to theisomerization uniti. This flow enables the isomerization of butene-l inthe second stage eiiluent prior to treatment with the selective solventand may eliminate the use of column 0 for separating olefin from then-butane recycle stream to the ilrst dehydrogenation stage.

Y However, in many instances, unless the isomerization catalyst is,carefully chosen, th instability ofthe diolefln favors butadieneremoval prior to isomerization. 1 v

Further, the ilrst stage condensate may," bepassed directly to theabsorption unit'through lines 32 and 34 for absorption of butene-2 priorto isomerization. of butene-I. This arrangementfavors the isomerizationreaction by-lowering .the butene-2 concentration in the feed to unit 5and may be employed when suitable absorption and fractionation capacityare available to obtain clean: separation of the somewhat greaterquantities of butene-l from butene2 and later from n-butane. l

selectivity in butylene production.

per pass conversion in order to maintain high While a great manydehydrogenation catalysts may be used, it is usually preferred'to employsolid contact catalysts comprising bauxite, synthetic aluminas ormagnesia, 'often bearing or promoted wlth.,metai oxides including thoseof chromium. nickel, 'zirf conium, tungsten, zinc, iron, and copper.

I'he conditions of pressure, i'low rate, etc., used in the paramn-oleiinconversion will depend largely on the activity of the catalyst and itsrange of maximum eiilciency. The charge vapors may, for example, betreated at temperatures of about 900 to about 1200 F. andnearatmospheric pressures, to obtain adequate conversion to butylenes.The vapors may be subjected totwo ormore successive treatments in aseries of catalyst chambers or sections containing catalyst of the sameor gradually increasing activity, or any portion of the vapors may berecycled with fresh lfeed to the catalyst. These and other knownoperating devices may be utilized to attain the desired conversion ofthe normal butane feed.

The dehydrogenation products are handled in conventional equipment tosegregate the components used in subsequent process steps. The customarymethods of cooling.: compressing, and fractionally condensing orabsorbing C4 hydrocarbons are suitable and may include one or morestages of compression followed by an oil absorption step or itsequivalent to absorb C4 hydrocarbons from the Cs and lower boilinghydrocarbons and fixed gases. The condensate later stripped from theabsorption oil may contain minor amounts of Ca hydrocarbons which may beremoved at. any suitable point in the processing stepsy For theisomerlzation'of butene-l to butenc-Z.

catalysts are chosen on the basis of their activity in the temperaturerange favorableto maximum butene-Z formation, and should not promotepolymerization or other undesirable' reactions which destroy or convertthe butylenes to unusable form. Since the equilibrium vbetween butene- 1and butene-2 favors maximum butene-2 concentration at low temperatures.catalysts ac.

s f 'rhs new diagrams ums ii'iusiratea and ae-v tive in the range ofabout 200 to about 600 F. are preferred.

Among the catalysts which have been found suitable for the isomerizationare several of an acidic nature; These include mineral materialscontaining acidic substances such as certain clays and silicates, saltssuch as aluminum phosphate and the like, or strong mineral acids insuitable concentration and often supported on adsorbent carriers. Inemploying catalysts of this type, precautions are observed to avoidundesired polymerization, as by regulation of the water content of thecatalyst and/or of the hydrocarbons.

Other types of catalysts which are active and often preferred are thosecomprising magnesia in natural or synthetic form. These catalysts havethe peculiar property of being highly active in substantially anhydrousstate, so that the feed, the catalyst mass, and the treating conditionsare regulated to produce and maintain substantially anhydrous conditionsFurther catalysts such as brucite after activating treatment to removewater and adsorbed gases', as described in the copending application ofDrennan, Serial No. 446,771, illed June 12, 1942,'are sufficientlyactive at temperatures in the range of about 100 to 'about 400 F. toenable substantially equilibrium isomerization at said temperatures. The

resulting butene-2 concentrations may amount to about 80-90 per cent ormore of the total normal butylenes in the feed to the isomerizationunit. Said catalysts are further characterized by low activity towardpolymerization, and may be employed, if desired, to treat hydrocarbonmixtures containing relatively large concentrations of butadiene and/orisobutylene without losses of said components.

The operation of the isomerization unit involves conventional equipment,and may consist of passage of the hydrocarbon fluid at suitable flowrates over a bed or through a bodyjof catalyst. The feed is ordinarilypreheated to operating temperature and may be substantially dehydratedwhen employing a catalyst most highly active in anhydrous state. Liquidphase contacting at relatively low flow rates is often preferred, andsuitable pressures may be utilized t prevent vaporization. In otherinstances. vapor phase contacting may be utilized at lower pressuresand/or higher temperatures. A

The eiiluent from the isomerization catalyst usually contains largeprODOrtions of unconverted normal butane which must be separated fromthe unsaturated components for recycle to the first stagedehydrogenation. butylene production is the principal object, it will bedesirable to limit the olefin content of this butane recycle stream'inorder to prolong cata-- lyst life and improve the reaction eillciency..In case of restrictions on the olefin content of the kbutane recycled,and in view of the benefits of "relatively complete butene-2 recovery.an absorpl ti'on operation utilizing a selective solvent is oftenpreferred to separate butene-2 as charge to the seconddehydrogenationstage.

However, when the rst stage condensate is treated over a highlyefiicient isomerization catalyst, the unconverted butene-1 concentrationmay be reduced so low that the butane and lighter fraction separatedfrom butene-2 by fractionation may be recycled satisfactorily to thenrst stage dehydrogenation..

'Theuse of certain selective solvents for thev present process isparticularly advantageous because th'e solvents while exhibitingsuitable pref- In many cases, whenv low one atmosphere.

`further treatment for olefin separation. In other cases, supplementalbutene-1- separation and/or isobutylene removal may be desirable.

In the second dehydrogenation stage, the conversion of butene-2 tobutadiene is usually carried 'out' at temperatures of about 1100 toabout 1300 F., near-atmospheric pressures, and with butene partialpressures in the charge 'vapors be- A convenient method of operationwith reduced butene partial pressures involves -the use lof an inertdiluent, preferably steam, with the butene-2 charge to regulate thebutene partial pressure and space velocity in the catalyst zone.

Catalysts for the -second stage dehydrogenation are in general lessactive than those employed in the first stage and may be pretreatedand/or compounded with various materia to impart resistance to poisoningby water vapor and to suppress polymerization and cracking reactions atthe high temperatures employed.

unconverted butene-2, butene-1, and isobutylene formed by isomerizationof the butene-2 charge, and traces of butane produced over the catalystmay be first fractionated to separate some of the butene-2 and heaviermaterial to facilitate the solvent absorption step.

The course of the absorption operation is sub- 'stantially the same asthat described for'the first stage condensate, with butadiene absorbedalong vwith butene-2. VComplete separation of butane is essential to therecovery of high purity butadiene. The butene-1 and n-butane whenprocessed over the isomerization catalyst are handled in the samefashion as the components of the first stage condensate. Isobutyleneremoval may systemi be practised at any point subsequent to the solventabsorption step, and is preferably carried out at the stage where theisobutylene concentration reaches a maximum.

, The butadiene-butene-Z extract recovered from the solvent 'isseparated into its components by precise fractionation, yieldingsubstantially pure ybutadiene and butene-2 for recycling to the secondstage catalyst after combination with the other butene-2 streams fromother parts of the This inethod of supplying butene-2 as feed to thedehydrcgenation operation producing buta"` 'l diene Venables a moreselective conversion' even under more severe conditions than when amixed butylene feed 'or butene-l alone is` employed, This is apparentlydue to the greater stability;

of the carbon skeleton of butene-z as compared to butene-l and to theconsequent-higher ultimate yields of butadiene and decreased losses ofbutylene feed in the form of light gases and car-` bon. Thus, thepresent process makes possible higher per pass conversions and/or higherb utadiene yields from equivalent amounts of butylene feed stocks byvirtue of the isomerization of butene-l and the selective recovery ofbutene-2.

In view of the above-described operations and the advantages obtained,the benefits of the present process will be obvious. The sequencev ofthe various steps and the selection of operational schemes such as areillustrated in the lflow dia- Y grams lwill depend on process economicsfor each individual plant. Some further illustration of the principlesand operations of the process may,

however, be provided in the following exemplary operation, substantiallyas shown in kFigure l.

Normal butane may be dehydrogenated` over Ca and lighter Butene-l 12413Butene-2 23-24 n-Butane 61-62 After substantially complete dehydration,isomerization of this condensate over activated brucite catalyst attemperatures of Z50-300 F. produces a composition as follows:

Q, Mo'l per cent Ca-and lighter 2-3 Butene-l 2-3 Butene-Z 33-34 n-Butane61-62 When the isomerized c ondensate is contacted inv a liquid-liquidabsorption operation with furfural as the selective solvent, thefollowing sepa- -ration of raffinate from extract is accomplished: v

, Raillnate, Extract, mol

mol per cent per cent Ca and lighter 8-4 1-2 Butane-1 3-4 Buteue-2 95-96n-Butane 92-93 2-3 'I'he raiinate may be recycled directlyto then-butane dehydrogenatlon step while the butene-2 is used as a portion ofthe feed to the second stage of dehydrogenation.

alumina-chromium oxide type catalyst to con- After a. preliminaryfractionation to remove a portion of the butene-Z and heavier material,`the condensate is contacted with furfural in an absorption step, andthe ramnate and extract show the following separation:

Rafllnate, Extract, mol

mol per cent peroen C; and lighter 16 Butadiene 68-70 Isobutylene-- 7Butane-1...-. 50-60 Butane-2.. l-Z) Sil-32 Butane 5-6 Fractionation ofthe extract produces butadiene of 97-99 per cent purity. The butano-2also produced is combined with that recovered `by stripping Cs andheavier from the preliminary con-r-y densate fractionation and thatproduced from the rst stage condensate togive a feed stock containingover 95 mol per cent of butene-2.

TheV raffinate is depropanized to continuously separate and vent asubstantial portion of the C:

and lighter material, and treated over a selective.

polymerization catalyst to effect isobutyiene re,- moval. The adjunct ofthe polymerization step -is a fractionation operation which separates Csand heavierliquid from the C4 raflnate.

When added to the first stage condensate ahead Aof the isomerizationunit, the composition of the combined stream is approximately asfollows:

Mol per cent C: and lighterv 2 Isobutylene 2 Butene-l 35-40 Butene-25;-10 n-Butane 51 arated to the isomerization unit, preferably byzaddition ahead of the depropanizer of the isobutylene removal unit.

When the above described operation is altered to incorporate the flowoil-Figure 2, the composition of product streams is not greatly changed.The principal variation is the increased fractionation load for unit `9separating butene-l from n-butane with greater precision.-

From the foregoing, it will beapparent that the isomerization ofbutene-l to butene-2 at the indil cated points in the two-stagedehydrogenation The butene-2 may be diluted with steam to produce acharge mixture with a steam-butene molar'ratio of three or somewhathigher and,

dehydrogenated over bauxite bearing barium hydroxide at '1200 F. toconvert 30-40 per cent of the butene-2 per pass. The C4 condensaterecovered from the 'dehydrogenation products will have the followingapproximate composition:

Mol per cent C3 and lighter '7.5 Butadiene 16-17 Butylenes '72-73 Butanev 3 05+ f 0.5

system enables the more efficient and economical operation ofthebutylene segregation and butadiene 'purication steps. Of particularimportance are the reduction in .the number and sizer of precisefractionating units which are otherwise required for butene-lseparation, and the `added benefits of charging substantially only.

butene-Z to-the second stage dehydrogenation.

In case the butylenes for the olefln-diolefin conversion are availablefrom a source other than n-butane dehydrogena'tiom the process of thisinvention is applicable to the treatment of anybutane-butylene mixturewith, perhaps, suitable revisions for handling larger quantities ofisobutylene and different disposal of the parailins discarded from thesystem. Such revisions may include the use of a single catalyst end/orreagent to eilect isobutylene removal and butene-l isomerization asdescribed in our` copending applica- Aprocedure maylbe followed in thetreatment of C hydrocarbons for-the production of pentadienes. Normalpentane may be dehydrogenated in a rst step'forming normal pentenesincluding pentene-l and 2-pentenes, the pentene-l isomerized toZ-pentenes, and the pentene2 separated for dehydrogenation in a secondstep to produce pentadiene. The pentene-l formed in the seconddehydrogenation may be separated from the eiliuent and passed to theisomerization step. The various streams may be handled in the samemanner as the C4 streams, hereinafter more fully discussed in detail,and this application of the invention will be evident to those skilledinthe art.

These and other modifications and extensions of the present inventionwill be obvious in the light of the disclosure and speciiic descriptionsprovided. Therefore no limitations are implied except as defined in thefollowing claims.

We claim:

l. The process for the production of a dioleiin of four to five carbonatoms per molecule from the Acorresponding normal parailin whichconiprises catalytically dehydrogenating said paraffin under conditionseffecting conversion of a substantial portion of the normal parailin tothe corresponding oleiins including the 1-olenn -and 2- oleflns;catalytically isomerizing the olens in the effluent of thedelrvdrogenation step under conditions effecting conversion of at leasta portion of said 1-oleiln to 2olefins as the principal reaction;separating the 2-olens from the 1-olefin and unconverted parailln in theeiiluent of said isomerization; recycling the unconverted parailin tosaid dehydrogenation; catalytically dehydrogenating said Z-olenns underconditions effecting conversion 'of a substantial portion of said 2-olens to the corresponding diolefin with the simultaneous formation ofsome of the l-olefin;

` separatingA the dioleiin and unconverted 2 -olefln in admixture fromthe l-olefin in the eiliuent of said olen dehydrogenation step, treatingthe' r mixture of dioleiin -an`d unconverted 2oleiin to separate sameinto a fraction of substantially pure diolen and a fraction of theunconverted 2-olen, and recycling theunconverted Z-oleflns to the oleiindehydrogenation step. Y

2. The process for the production of a 'diolen of 4 to 5 carbon atomsper molecule from the corresponding normal parain which comprisescatalytically dehydrogenating said parailin in a first dehydrogenationstep forming the corresponding oleilns comprising the l-olefln and 2-oleilns; catalytically isomerizing the olefins in the eilluent of thedehydrogenation step under condiy tions effecting conversion of at leasta portion of said 1-olen to -2-olens as the principal reaction;separating the Z-olens in the eiliuent ofthe isomerization step fromunconverted Dlf' and unconverted l-oleiin; separating the parafn fromthe l-olen; recycling the paratl'in to the first dehydrogenation step;recycling the uncon verted l-ole'iin to the isomerization step;catalytically dehydrogenating said 2-oleiins in a second yldehydrogenation step formingthe corresponding dioleiin with thesimultaneous formation of the 1'o lenn; separating 'the diolen andunconverted 2-olens from the l-oleiin in the effluent of the seconddehydrogenation step; passing the l-oleiin to the isomerization step:separating the dioleiivn in substantially pure form from 'theunconverted 2-oleflns; and recycling the unconverted 2-o1efin to thesecond dehydrogenation step.

3. The process for the production of a dioleiin of four to five carbonatoms per molecule from the corresponding normal paraffin whichcomprises catalytically dehydrogenat-ing said paranin in a rstdehydrogenation step, forming the corresponding olens comprising thel-olen and 2-olefins with the simultaneous formation of thecorresponding isooleiin and diolen; catalytically isomerizing theoleflns in the eliiuent of the dehydrogenation step under conditionseffecting conversionv of at least a portion of said 1olefln to 2-o1eiinsas the principal reaction; separating the 2-olens'and' the dioleiin inthe eilluent of the isomerization step from the unconverted normalparaln, the isooleiin, and the unconverted l-oleiin; segregating theunconverted normal parailin, the l-olefln, and the isooleiin; recyclingthe unconverted normal parain to the'irst devhydrogenation step;recycling the unconverted .l-olen to the isomerization step; withdrawingthe isooleiin from the system; separating the diolen from the 2olens ina -second separation step; catalytically dehydrogenating said .'Z-ole-Vfins in a second `dehydrogenation step forming the corresponding diolenwith the simultaneous formation of the l-oleiin and isooleiin;separating the diolen and unconverted 2-o1eiins from the l-olefin andisooleiin in the .eilluent of the second dehydrogenation' step;separating the 1- oleiin from the isooleiin;' withdrawing the isoolenfrom the system; passing ythe 1-o1en to the isomerization step;separating the dioleiin in substantially pure form from the unconverted2- olens; and recycling the unconverted 2-oleiins to the seconddehydiogenation step.

4. 'Ihe process for the production of pentadiene from normal pentanewhich comprises catalytically dehydrogenating normal pentane underconditions eiecting-conversion of a substantial portion of the normalpentane to the corresponding pentenes including pentene-l and the2-pentenes; catalytically isomerizing the oleiins in the eiiluent of thedehydrogenation step uiider conditions effecting conversion of at leasta portion of said pentene-l to pentene2 as the principal reaction,separating the pentene2 from the pentene-l' and unconverted normal-pentane in the eiiluent of said isomerization step, separating thepentene-l from the unconverted normal pentane, passing the pentene-l tothe isomerization step, recycling the unconverted normal pentane to thedehydrogenation step, catalytically dehydrogenating the vsaid pentene2under conditions effecting conversion of a substantial portion ofsaid'pen tene-2 to pentadiene withthe simultaneous formation of somepentene-L separating pentadiene and unconverted pentene2 from the pen-Atene-l in the eilluent of said last-mentioned dehydrogenation step,separating substantially pure pentadiene from the Vunconverted pentene2,recycling the unconverted pentene2 to said lastmentioned dehydrogenationstep, and passing the pentene-'l to the isomerization step.

5. 'I'he process for the production of butadiene from butane whichcomprises catalytically dehydrogenating normal butane under conditionsetfecting conversion f a substantial portion of the normal butane to thecorresponding butenes including butene-l and the Z-butenes,catalytically isomerizing the olenns in the eiuent of the ydehydrogenation step under conditions effecting conversion of at least aportion of said butene-l to butene-2 as the principal reaction,separating the butene-2 from the butene-1` and unconverted normal butanein the eiiluent 'of said isomerization step, separating the butene-lfrom the unconverted normal butane, passing the butene-l so separated tothe isomerirati'on step, recycling the unconverted normal butane to thedehydrogenation step, catalytically dehydrogenating the bi1- tene-Zunder conditions eiecting conversion of a substantial portion of saidbutene-2 to butadiene with the simultaneous formation of some butene- 1,separating butadiene and unconverted butene- 2 from the butene-l intheeiilue'nt of said lastmentioned dehydrogenation step, separatingsubstantially pure butadiene from the unconverted the butadiene from theunconverted butane-2; and recycling the unconverted butane-2 to thesecond dehydrogenation step.

8. The process for the production of butadiene from normal butane whichcomprises catalytically dehydrogenating normal butane in a firstdehydrogenation step, forming butene-l and 2-butenes with thevsimultaneous formation of butadiene and isobutene; catalyticallyisomerizing the butenes in the eiiluent of the dehydrogenation stepunder conditions eecting conversion of at butene2,recyc1ing theunconverted butene-2 to said last-mentioned' dehydrogenation step andVpassing the butenesl to the isomerization step.

6. The process for the production of butadiene from normal butane whichcomprisesJ catalytically dehydrogenating normalbutane in a rstdehydrogenation step forming butene-l and 2-butenes with thesimultaneous formation of butadiene; catalytically isomerizing thebutenes in the eiiluent of the dehydrogenation step under conditionseffecting conversion of at least a portion of said butene-l to butene-2as the principal c 'verted butene-2 from the butene-l in the eiiluent ofthe second Adehydrogenation step; passing the butene-l to theisomerization step; separating the butadiene from the unconvertedbutene-2; and

`least a portion of said butene-l to 2butenes as the principal reaction;separating butene-2 and the butadiene in the iiluent of theisomerizationstep from unconverted normal butane, isobutene, andunconverted butene-l; segregating the normal butane, isobutene, and thebutene-l; recycling the uneonverted normal butane to the rstdehydrogenation step; recycling the unconverted butene-l to theisomerization step; withdrawing the isobutene from the system;separating the butadiene from the butene-2; catalytioallydehydrogenating the butane-2 in a second dehydrogenation step formingbutadiene with the simultaneous formation of butene1;separating thebutadiene and the unconverted butene-2 from the butene-l in the eilluentof the second dehydrogenation step; passing the butene-l to theisomerization step; separating the butadiene from theunconvertedbutene-2); and recycling the unconverted butene-2.to the seconddehydrogenation step.

recycling the unconvert'ed butene-2 to the second f dehydrogenationstep.

y7. The process for the production ,of butadiene from normal butanewhich comprises catalytically dehydrogenating normalbutane in a firstdehydrogenation step forming butene-l and butene- 2 with thesimultaneous formation .o f butadiene;

catalytically isomerizing the butenes in the ef` fluent ofdehydrogenating step under conditions effecting conversion of at least aportion of said butee-l to 2-butenes as the principal reaction;v

separating the Z-butenes and. butadiene inthe v eilluent of theisomerization step from unconfverted normal butane and unconvertedbutane-1; separating the normal butane from the butene-l;

recycling the unconverted normal butane to the drawing the isobutenefrom the system; passing the butene-l to the isomerization step;separating 9. The process for the production of butadiene.

from normal butane. which comprises catalytically dehydrogenating normalbutaneunder conditions eifecting conversion of a substantial portion ofthe normal butane to normal butenes including butene-l and Z-butenes;catalyticallyisomerlzing the butenes in the eiliuent of thedehydrogenation step undericonditionsA effecting conversion of at lea'sta portion of said butene-l to 2-butenes as the principal reaction;contacting the eiiiuent of said isomerization with a selective solventeffecting removal of lbutane-2 from the butene-l ,and unconverted normalbutane; recycling the unconverted normal butane to the saiddehydrogenation; catalytically dehydrogenating the butene-2 underconditions effecting conversion of a substantial portion of saidbutene-Z to buta- 1 diene with. the simultaneous formation of butene-1'; contacting the eiiluent oi' said last-mentioned dehydrogenation witha selective solvent effecting removal of the butadiene and the butene-2from the butene-l therein; passing the butene-I to the isomerization;separating butadiene from the unconverted butene-2; and recycling theunconverted butene-2 to said last-mentioned dehydrogenation.. A

10. The process for the production of butadiene from normal. butanewhich comprises catalytically dehydrogenating normal fbutane underconditions effecting conversion of a substantial portion of the normalbutane to the butenes includingbutene-l and 2butenes with thesimultaneous formation of butadiene; catalytically Qisomerizig thebutenes in the euent of the de- \\hydrogenation step under conditionseffecting conversion of at least a portion of said butene-l to 2-butenesas the principal reaction; contacting the eiiluent of said isomerizatlonstep with a selective solvent in a separation step eiecting removal ofthe Z-butenes and the butadiene from the butene-l and unconverted normalbutane therein; recycling the unconverted normal butane to said firstdebydrogenation step: separating the butadiene from the butene-2;catalyticaliy dehydrogenating the butene-2 under conditions effectingconversion of a substantial portion of said butene-2 to butadiene withthe simultaneous formation of butene-1; separating at least a por--ition'of the unconverted butene-2 from the butadiene and butene-1 in theeiliuent of the second dehydrogenation step; recycling the unconvertedbutene-2 to the second dehydrogenation step; and passing the butadieneand. butene-1 tothe firstmentioned vseparation step.

11. The process of producing butadiene from vnonxnal butane whichcomprises catalyticaily dehydrogenating noi-mal butane' to normalbutenes including butene-1 and butene-2 in a rst dehydrogenation stage,segregating a predominantly C4 hydrocarbon fraction from the eiiiuent,said fraction containing the butane and butene content of said eiiiuent,passing said fraction through a catalytic isomerization step and therebyetlecting isomerization of said butene-l to,

the rich solvent. fractionally distilling the C4 hydrocarbon fractionfrom the eiliuent, said stripped butadiene and butene-2 to produce anoverhead of substantially pure butadiene and a bottoms of butene-2, andrecycling the butene-2 content of said bottoms to said seconddehydrogenation step.

12. The process of producing butadiene from normal butane whichcomprises catalytically dehydrogenating normal butane to normal butenesincluding butene-1 and butene-2 in a first dehydrogenation stage,segregating a predominantly feed to the extraction step while allowingthe butene-2 as substantially theV sole reaction, ex-

tracting the isomerization eilluent with a selective solvent having`preferential solubility. for butene-2 as compared to butene-1v andthereby eiecting solution of the butene-2 content while allowing thenormal butane and butene-1 content to pass through undissolved,recycling the undissolved normal butane to said dehydrogenation step,stripping the dissolvedbutene-2 from therich solvent, catalyticallydehydrosenating the stripped butene-2 to butadiene in a seconddehydrogenation stage with the simultaneous for- `mation of somebutene-1, segrgating-a C4 hydrocarbon fraction from the eiiiuent, saidfraction containing the butadiene and butene-1 content and at least aportion of the butene-2 content of said eiiiuent, extracting saidfraction with a selective solvent having preferential solubility forbutene-2 as compared to butene-1 and thereby effecting solution of thebutadiene and butene-2 content while allowing the butene-1 content tosolved'butene-i to said isomerization step, stripping the dissolvedbutadiene and butene-2 from normalbutane and butene-1 content thereof topass through undissolved, fractionally distilling the raffinate fromsaid extraction step to segregate an overhead of butene-1 and a bottomsof normal butane and recycling said butene-l to said isomerization stepand said normal` butane to said dehydrogenation step, stripping thedissolved butene-2 and butadiene from the rich solvent,

` fractionaliy distilling the stripped butadiene and ypass through.undissolved, recycling the undis-v 5 butene-2 to produce an. overhead ofsubstantially pure butadiene and a bottoms of butene-2l catalyticallydehydrogenating said butene-,2 to butadiene in a second hydrogenationstage with the simultaneous formation of some butene-1, seg? regating aC4' hydrocarbon fraction from the efuent, said fraction containing thebutadiene, norinal butane and Abutene-1 content and at least a portionof the butene-:2 content of lsaid efv fluent, and commingling saidfraction with said isomerization eilluent and, extracting it andotherwise treating it therewith as above.

WALTER A'. sCHULzE. JOHN c. mmm.

